HNO has distinctive roles in many biological processes, such as vascular relaxation, enzyme activity regulation, and neurological function regulation. Its pharmacological effects include enhanced cell oxidative stress, blood-brain barrier disruption and neutrophil infiltration during renal ischemia/reperfusion. The preferential vasodilative effect exhibited by HNO compared to its sibling signaling molecule NO makes HNO donors a potential new class of vasodilators and heart failure treatments. Many of the biological effects of HNO are involved with heme proteins and other metalloproteins. Structural information of the HNO protein complexes is necessary for understanding the physiological and pharmacological functions of HNO. However, there are currently no crystal structures of HNO protein complexes. The overall objective of this work is to investigate the structure, characteristic spectroscopic data, and the roles of metal and active site in the only isolated HNO protein complex, MbHNO (Mb = myoglobin), and related heme protein complexes and HNO metal complexes using high accuracy quantum mechanics methods. The first specific aim is to establish quantum chemical methods that can accurately reproduce the broad range of experimental NMR shifts and vibrational frequencies seen in HNO metal complexes, including heme protein model systems, and determine the effects of metal and ligand set on the HNO stability and spectra. The second specific aim is to conduct a comprehensive investigation of possible active site models of MbHNO, with different hydrogen bonding modes for the HNO moiety, different scales of nearby residues, and different ligand orientations. A geometric structure that quantitatively agrees with experimental NMR, vibrational, and X-ray absorption spectroscopic data will be determined for MbHNO. Effects of HNO interactions with nearby residues in the active site on the MbHNO geometry, HNO stabilization energy, and spectroscopic properties, as well as comparisons with MbNO, MbO2, and RNO (R = alkane and arene) heme protein complexes will be examined to improve our understanding of the functional role of the active site. Results will provide useful details of the structural, spectral and functional aspects of HNO interactions with metal centers in proteins and models, which will assist in future studies of health, diseases, and therapeutic treatments involving HNO. PUBLIC HEALTH RELEVANCE: This project will provide useful details of structural, spectral and functional aspects of HNO interactions with metal centers in proteins. Since HNO participates in a broad range of physiological processes related to health, has extensive pharmacological effects, and offers a promising new treatment for diseases such as heart failure and stroke, results from this project will assist future studies of health, diseases, and therapeutic treatments involving HNO. [unreadable] [unreadable] [unreadable]